How smart is the layout in your metal fabrication plant?

May 27, 2023

Chris Ryan/OJO Images

What does it mean to be smart? A smart person has or shows quick-witted intelligence. A smart machine is any device programmed to be capable of some independent action. A smart facility uses technologies like Industrial Internet of Things (IIoT), big data, artificial intelligence, and digitization to optimize and track a facility's performance and overall efficiency.

So, what exactly makes a custom fabricator's layout smart? A custom fabricator has a smart layout when its design maximizes unidirectional flow and minimizes the cost of that flow. It's the foundation of an effective production system. A plant's layout affects how everything flows through the system—raw material, work in process (WIP), personnel, visitors, suppliers, customers, machinery, fixtures, tools, and information.

Some of the best facilities in custom fabrication use a combination of functional and cellular layouts. In the cellular portion of the shop, each stand-alone, flexible cell produces a family of similar parts with common, if not identical, process requirements. Do you know the part families in your product mix?

The best layout design for any facility also considers all secondary processes, like deburring and hardware insertion. For instance, a cell might have mobile carts with tools required to perform those secondary processes when and where they’re needed.

Also, preproduction or prototyping work should be done in a separate section of the facility. One-off and intermittent (or sporadic) work is essentially an extreme case of high-mix, low-volume manufacturing. At least one smart custom fabricator has a separate rapid response cell that helps to reduce disruptions to high-to-medium-volume production caused by short runs of nonrepeating parts.

Batch-and-queue production is the curse of a purely functional layout. Imagine the damage to three business objectives—WIP control, throughput, and on-time delivery—if material yield and batch-and-queue production were in play at each department (plasma cutting, bending, welding) in a shop's functional layout. Now imagine the flow in a smart facility layout using cells. Software nests all the needed parts to make a single weldment (or batch of that weldment) in a cell. A plasma cutter burns the parts. A gantry robot or other mechanism then places all the parts on the deburring station. The operator deburrs the parts and places them in the welding fixture. He then prompts the arc welding robot to create the weldment. That same operator inspects the work and grinds off any weld spatter. Every operation needed to produce a weldment sent to the assembly line is done in one cell.

Manufacturing cells act as the basis for employee cross-training. For example, a cross-trained operator in a one-person fabrication cell could work side by side with one or more cobots that do the tasks that are 3D—that is, those tasks that are dirty, dull, or dangerous. Cross-training guarantees an increase in the ratio of machines to operators in any cell. It also increases the velocity of all material and information flows in the facility and helps keep the bottleneck machines utilized at about 85%. Above all, with operators able to move between different cells, the shop has the flexibility to adapt to changes in demand for parts produced in the cells.

Machine utilization cannot supersede WIP control, throughput, and on-time delivery—except at the bottleneck machine in a cell or in a bottleneck work center for the entire shop. Too many custom fabricators are slaves to the obsolete practice of utilizing every machine (and its operator) to the max, regardless of the WIP this creates across the facility. WIP is a form of inventory, and inventory is an asset, right? Wrong. Inventory is one of the seven forms of waste.

This is why material utilization shouldn't be treated in isolation from machine utilization, labor utilization, WIP control, throughput, and on-time delivery. For instance, to increase sheet yields, most fabricators "cut ahead," either by looking ahead into the schedule or using filler parts. They also attempt to order right-sized sheets and plates for typical runs.

A cellular layout's increased flow velocity must be complemented by shop floor management based on a daily schedule produced by finite capacity scheduling software. In addition, the daily schedule must be executed, monitored, and updated using a combination of a machine monitoring system and a worker connectivity platform that helps employees communicate as needed.

This is where the water spiders who handle all factory logistics enable the rest of the shop floor employees to be engaged. It's not enough just to have a great work ethic that binds and motivates all employees to meet or beat the daily schedule. They need to have new work brought to them in time. They need to have their completed work taken away and delivered to the next work center in time. They need questions about tooling, quality, fixturing, and other resources to be answered in time. Any smart custom fabricator will have one or more water spiders who do more than mundane material handling tasks.

Scheduling itself should be tailored for the realities of the job shop. Consider the classic Kanban system for pull scheduling, which prevents upstream work centers from starting new orders until downstream work centers have reduced their queue of jobs to the reorder point. The job shop alternative to pull scheduling is the practice of work order release (WOR). Think of every order released to the shop floor as being a kanban.

Fabricators can implement WOR using the simple drum-buffer-rope concept from the Theory of Constraints, or they can take an advanced approach using finite capacity scheduling. The latter approach uses a combination of forward and backward scheduling at the bottleneck machine or work center to determine the sequence and timing for release of every order into the facility. Also, a smart custom fabricator will have a qualified full-time production scheduler on staff.

A facility layout is smart when outside service providers (OSP)—powder coaters, heat treaters, electroplaters—are treated as an extension of the facility. Every provider is included as a work center in the production schedule. This gives either party (the custom fabricator and its OSP) complete visibility into how their schedules influence and interact with others.

Such all-inclusive shop schedules can prove especially beneficial for a fabricator managing any long-term agreements for parts or products. A fabricator and its service providers could even form a consortium for sharing best practices.

Flexibility should not be limited to rapid changeovers on individual machines like press brakes and machining centers. In a broad sense, flexibility in a smart facility layout comes in several forms.

First is the most familiar: setup flexibility, when individual assets can change over rapidly from one job to another.

Then there's process flexibility, when available resources (machines, people, tools) and systems can make a variety of parts with different specifications.

Routing flexibility allows for the same part to be made using any one of several different routings. With mix flexibility, a shop can simultaneously process a large variety of parts requiring different materials, vendors, and tolerances.

Volume flexibility accommodates variability in the order quantities for the same or different parts or products. Such variability increases when the same facility seeks to produce parts in different phases of their lifecycle.

Finally, there's facility flexibility, which allows the entire facility to be reconfigured quickly if changes in the mix or volume occur. This includes having mobile equipment, usually for secondary processes, that can be rapidly relocated on demand to any location in the facility.

Does your custom fabrication shop's layout possess all of these different types of flexibility that any job shop must have? Investments in manufacturing automation, inspection, and other process-related technology should be matched with investments in material handling, parts tracking, and the IT systems in use all over your factory. These are the foundational, essential, industrial, and production engineering details that are at the core of any production system!

A smart investment in software and automation must improve important metrics like safety, quality, delivery, and cost, computed for all significant flows in the facility layout—not just the flows of raw material, WIP, and finished goods, but also the flows of people and information. Information flow can include anything that eliminates the need for manual data entry; after all, every keystroke presents a potential for error, and every material handling mistake can add up to a lot of wasted time. Technology like augmented reality, handheld ID scanners, and pick-to-light systems (where lights indicate which products or material water spiders should pick) can help visually select, monitor, measure, and control WIP.

A custom fabricator's facility layout is smart when assemblers receive all the parts they need to start on time per the schedule. "Complete" means that, per the bill of material (BOM) for that product, the water spider did the milk run to collect all the in-house parts produced in different cells as well as the purchased parts stored in the parts supermarket adjacent to the assembly department. Without a daily schedule produced by finite capacity scheduling software and an accurate, complete BOM in the ERP system, the milk run could result in an incomplete kit of parts.

A smart yet simple approach to ensure the completeness of kits delivered to assembly is to use visual Kanban systems. For instance, one fabricator in Columbus, Ohio, has used "kit carts" specially fabricated to carry the complete mix of parts in the right quantity to weld and assemble a certain number of frames. Once all those components were used, the water spider rolled the cart back to an empty white square painted on the floor, adjacent to the sheet metal shop. Those squares were the inventory buffer linking assembly with the sheet metal shop.

So, would you like to know if your facility has a smart layout? Buy a set of medium-point Sharpies in at least 20 different colors. Print a drawing of your current layout. Select a sample of at least 20 products. If you make custom variants of the same product, you can map the complete indented bill of material (IBOM) for the standard product variant. But if you are a classic job shop that makes a variety of different products, you can perform a product-quantity-revenue (PQR) analysis and pick a few products in that 80-20 sweet spot of the Pareto curve.Now, pick a part from the sample you just identified. Select any one of those Sharpies and trace its routing, operation by operation.

Continue until you’ve traced the routing of every part in the sample. Congratulations, you have produced a spaghetti diagram!

So, what do you see in the spaghetti diagram you just created? Long arrows? Crisscrossing arrows? Many arrows entering and leaving a particular department? Bidirectional arrows (that is, jobs that backtrack or move back and forth between departments)? Arrows with zero line of sight (LOS)? That is, neither of the operators at the two work centers connected by an arrow with zero LOS can determine when to send or expect work from the supplier or customer work centers, respectively.

Know that when it comes to designing a smart facility layout, all this merely scratches the surface. Other factors include where and how to integrate the inspection function, as well as which specific multifunction machines to buy to reduce material flows and improve processes. Regardless, the core principles behind these ideas are the same: Look beyond the machines you buy and the technology you install.

Consider a scenario in which managers and employees at a fab shop focus only on machine uptime and utilization efficiency. Doing this, they ignore the costs, quality problems, and production delays from transfers between every pair of consecutive operations in the routing of every product they make—in other words, all those lines on the spaghetti diagram you just drew.

Assume you have all the foundational elements in place. At work centers that aren't bottlenecks, you focus on WIP control and flow velocity, not machine utilization. You use metrics like bottleneck machine utilization, throughput, and revenue-earning velocity. You schedule strategically. You design multiprocess cells, and you cross-train the employees who work in them. You empower them to determine who moves out of their "host cell" to go work in other cells that lack sufficient operators or where demand has increased.

Your spaghetti diagram is your lighthouse that will guide you to the foundational elements of a successful custom fabricating production system. Your shop has unique attributes, of course. But in many cases, the more you can do to make that spaghetti diagram less tangled for the as-is material flows in your facility, the smarter your facility layout is likely to be. Technology alone will not get you there!